CN111718713B - Carbon dots and their preparation methods and applications, solid luminescent excipient materials - Google Patents

Abstract

The invention discloses a carbon dot, a preparation method and application thereof, and a solid luminescent forming material. The preparation method of the carbon dots comprises the following steps: dissolving and mixing the carbon dot preparation raw materials in a solvent, and removing the solvent capable of reacting with the dehydrating agent. Adding a dehydrating agent into the uniform mixture, and reacting at the temperature of 80-200 ℃; the carbon dot preparation raw materials contain hydrophilic groups, the carbon dot preparation raw materials are fully and uniformly mixed in a dissolving mode, basic conditions are provided for reaction effects, in addition, in the reaction process, the hydrophilic groups contained in the raw materials are subjected to condensation polymerization under the action of the dehydrating agent, water-soluble and hydrophobic carbon dots can be simultaneously generated in the reaction process, and the synthesis ratio of the water-soluble and hydrophobic carbon dots can be realized by controlling the using amount and the type of the dehydrating agent. In addition, the whole preparation process is simple to operate, the wavelength of the synthesized hydrophobic carbon dots is long and adjustable, and the fluorescence quantum yield of the carbon dots is high.

Description

Carbon dots and their preparation methods and applications, solid luminescent excipient materials

technical field

The invention relates to the technical field of nanomaterials, in particular to a carbon dot, its preparation method and application, and a solid luminescent excipient material.

Background technique

Carbon dots (CDs) are a new class of fluorescent nanomaterials, which have attracted extensive attention from researchers due to their easy surface functionalization, good biocompatibility, stable chemical properties, strong resistance to photobleaching, abundant raw materials and easy preparation. . Carbon dots have gradually shown potential to replace conventional quantum dots in applications in drug delivery, medical diagnosis, two-photon imaging, ion detection, and catalysis.

So far, most of the synthesized CDs are water-soluble CDs. However, due to the limitation of their surface groups, such CDs are prone to the phenomenon of fluorescence quenching after aggregation (ACQ phenomenon), which is difficult to be applied in organic electronics, thin film applications or sensors in hydrophobic environments. Therefore, hydrophobic carbon dots (HCDs) have become a new research object for researchers.

At present, the methods of synthesizing carbon dots mainly include arc discharge, laser ablation, chemical oxidation in strong acid and electrochemical synthesis, and pulverize carbon allotropes, such as carbon nanotubes, nanodiamonds or graphite until the products produce fluorescent nanoparticles. characteristic. Among them, the main methods for preparing hydrophobic carbon dots are: firstly synthesize water-soluble CDs (WCDs), and then convert them into HCDs through surface modification, or prepare HCDs by one-step reaction at high temperature in strong acid, strong base or organic reagent. However, these preparation methods have disadvantages such as complex operation steps, long time consumption, reduced quantum yield, or strong toxicity and corrosion of solvents selected. In addition, the prior art also lacks a carbon dot preparation method that can simultaneously prepare water-soluble and hydrophobic carbon dots.

In view of this, the present invention is proposed.

Contents of the invention

The object of the present invention is to provide a carbon dot, its preparation method and application, and a solid luminescent shaping material, so as to improve the above problems.

The present invention is achieved like this:

In the first aspect, the embodiment of the present invention provides a method for preparing carbon dots, which includes:

In the homogeneous mixture of carbon dot preparation raw materials, add a dehydrating agent, and react at a temperature of 100-200 °C; wherein, the carbon dot preparation raw materials contain hydrophilic groups, and the homogeneous mixture is mainly obtained by the following preparation steps: The point preparation raw materials are dissolved and mixed in a solvent, and then the solvent capable of reacting with the dehydrating agent is removed.

In the second aspect, the embodiment of the present invention also provides a carbon dot, which is prepared by the above preparation method. Optionally, the carbon dot is a hydrophobic carbon dot separated after reaction.

In a third aspect, the embodiments of the present invention also provide the application of the above-mentioned carbon dots in the preparation of fluorescent materials.

In the fourth aspect, the present invention also provides the application of the above-mentioned carbon dots in the preparation of solid-state lighting devices, displays, or solid-state luminescent materials. The carbon dots are hydrophobic carbon dots separated after reaction. Optionally, the hydrophobic The carbon dots are N, S co-doped hydrophobic carbon dots with a fluorescence emission wavelength of 450-580 nm.

In the fifth aspect, the embodiment of the present invention also provides a solid luminescent excipient material, the raw material component of which contains the above-mentioned hydrophobic carbon dots.

The invention has the following beneficial effects: by first dissolving the carbon dot preparation raw materials and then removing the solvent capable of reacting with the dehydrating agent, the carbon dot preparation raw materials can be fully and uniformly mixed, providing basic conditions for the reaction effect of carbon dot generation, Then add a dehydrating agent to the homogeneous mixture, and then in the process of generating carbon dots in the reaction, the hydrophilic groups such as carboxyl, amino or hydroxyl groups contained in the carbon dot preparation raw materials can undergo polycondensation under the action of the dehydrating agent, so that the reaction The process can simultaneously generate water-soluble carbon dots and hydrophobic carbon dots. And the proportion of water-soluble carbon dots and hydrophobic carbon dots can be realized by controlling the amount and type of dehydrating agent. In addition, the whole preparation process is simple to operate, the synthesized hydrophobic carbon dots have a longer wavelength and can be adjusted, and the carbon dots have a high fluorescence quantum yield.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus It should be regarded as a limitation on the scope, and those skilled in the art can also obtain other related drawings based on these drawings without creative work.

Fig. 1 is the solid product photograph (the mixture of hydrophilic and hydrophobic carbon dots) of the second step synthesis of embodiment 1 of the present invention;

Fig. 2 is the solid product photo (mixture of hydrophilic and hydrophobic carbon dots) synthesized in the second step of Example 2 of the present invention;

Fig. 3 is the solid product photo (the mixture of hydrophilic and hydrophobic carbon dots) synthesized in the second step of Example 3 of the present invention;

Fig. 4 is the photo of the hydrophobic carbon dot solution of the embodiment of the present invention 1 under 365nm ultraviolet light irradiation;

Fig. 5 is the fluorescence emission diagram of the hydrophobic carbon dot synthesized in Example 1 of the present invention;

Fig. 6 is the ultraviolet-visible absorption spectrogram of the hydrophobic carbon dot synthesized in Example 1 of the present invention;

Fig. 7 is the XPS scan spectrum (i) of the hydrophobic carbon dot synthesized in Example 1 of the present invention, the peak spectrum (ii) of C1s XPS, the peak spectrum (iii) of N1s XPS, the peak spectrum (iv) of O1s XPS ) S2p XPS split peak spectrum (V);

Fig. 8 is the photo of the hydrophilic carbon dot solution synthesized in Example 1 of the present invention under 365nm ultraviolet light irradiation;

Fig. 9 is the fluorescence emission diagram of the hydrophilic carbon dot synthesized in Example 1 of the present invention;

Fig. 10 is the ultraviolet-visible absorption spectrogram of the hydrophilic carbon dot synthesized in Example 1 of the present invention;

Fig. 11 is the photo of the hydrophobic carbon dot solution in Comparative Example 1 of the present invention under the irradiation of 365nm ultraviolet light;

Fig. 12 is the fluorescence emission diagram of the hydrophobic carbon dot synthesized in Comparative Example 1 of the present invention;

Fig. 13 is the photo of the hydrophilic carbon dot solution synthesized in comparative example 1 of the present invention under 365nm ultraviolet light irradiation;

Fig. 14 is the fluorescence emission diagram of the hydrophilic carbon dot synthesized in comparative example 1 of the present invention;

Figure 15 is a white light lighting LED lamp constructed with hydrophobic carbon dots synthesized in Example 1 of the present invention as one of the light source components;

Fig. 16 is the electroluminescence spectrum diagram of the white light-emitting LED lamp in Fig. 12;

Figure 17 is a picture under natural light of the solid epoxy resin device loaded with the hydrophobic carbon dot of embodiment 1;

18 is a picture of a solid epoxy resin device loaded with the hydrophobic carbon dots of Example 1 under 365nm ultraviolet light irradiation;

Fig. 19 is a comparison photo of the hydrophilic carbon dot solution in Example 2 of the present invention under the irradiation of natural light and 365nm ultraviolet light;

Figure 20 is a fluorescence emission spectrum diagram of the hydrophobic carbon dots synthesized in Example 2 of the present invention;

Fig. 21 is a comparison photo of the hydrophobic carbon dot solution of Example 3 of the present invention under the irradiation of natural light and 365nm ultraviolet light.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that could be purchased from the market.

A carbon dot provided by the present invention, its preparation method and application, and solid luminescent shaping material are described in detail below.

The inventors analyzed the preparation methods of carbon dots in the prior art, and found that there is a lack of a synthetic method that can easily and simultaneously generate water-soluble carbon dots and hydrophobic carbon dots. There are two main methods for the preparation of hydrophobic carbon dots. One is to synthesize hydrophilic CDs (WCDs) first, and then convert them into HCDs through surface modification. For example, Shang and his colleagues dissolved WCDs in toluene and oleylamine and heated them under reflux at 130°C in an oil bath. After 6 hours, orange HCDs were obtained, and their emission wavelength (λem) was red-shifted by 20nm compared to WCDs; Varisco et al. obtained WCDs , and then add ethylenediamine or dodecylamine, and stir at 115°C for 4h to obtain HCDs whose wavelength does not change. This type of method has complex operation steps, takes a long time, and will reduce the quantum yield. Another type is the preparation of HCDs by one-step reaction at high temperature in strong acid, strong base or organic reagent. Commonly used reaction reagents include strong acids and bases such as phosphoric acid, nitric acid, and sodium hydroxide, or organic reagents such as toluene and 1-octadecene as solvents. And the reaction temperature of most experiments is between 160-280°C, and the reaction time is between 20min and 12h. However, due to the characteristics of strong toxicity and corrosiveness in the solvents selected by this method, they are not friendly to the environment and do not meet the characteristics of green synthesis.

Therefore, it is one of the main purposes of the present invention to develop a solid-phase synthesis method with simple and quick operation and an environmentally friendly process (reducing or not using strong acid, strong base and organic reagents) to obtain long-wavelength luminescent HCDs. Therefore, based on the current defects in the preparation of carbon dots, the inventor creatively proposed the following technical solutions through a lot of research and practice on the basis of the prior art.

Some embodiments of the present invention provide a method for preparing carbon dots, which includes: adding a dehydrating agent to a homogeneous mixture of raw materials for preparing carbon dots, and performing a reaction at a temperature of 100-200°C. Wherein, the carbon dot preparation raw material contains hydrophilic groups, and the homogeneous mixture is mainly obtained by the following preparation steps: dissolving and mixing the carbon dot preparation raw material in a solvent, and then removing the solvent capable of reacting with the dehydrating agent.

By dissolving the raw materials for preparing carbon dots first, and then removing the solvent that can react with the dehydrating agent, the raw materials for preparing carbon dots can be fully mixed evenly, and the solvent will not react with the dehydrating agent to affect the synthesis of carbon dots process. It should be noted that the removal of the solvent in the embodiment of the present invention can also be basically removed, and it should be ensured that a small amount of residual solvent will not affect the carbon dot synthesis process, and a better way is to completely remove it. When the solvent is not reactive with the dehydrating agent, the solvent removal step is not an essential step.

Further, in the process of generating carbon dots, the dehydrating agent can promote the polycondensation of hydrophilic groups such as carboxyl, amino or hydroxyl groups contained in the raw materials for carbon dot preparation, promote the synthesis of carbon dots, and realize water-soluble carbon dots And the preparation of hydrophobic carbon dots, and in the synthesis process, water-soluble carbon dots and hydrophobic carbon dots are synthesized at the same time, but the main body is hydrophobic carbon dots. The ratio of water-soluble and hydrophobic carbon dot synthesis and the wavelength of hydrophobic carbon dots can be realized by adjusting the amount and type of dehydrating agent. That is, the more dehydrating agent is used, the less water-soluble carbon dots are synthesized, the proportion of hydrophobic carbon dots increases and the wavelength red shifts.

The longer the reaction time and the higher the reaction temperature, it is beneficial to the preparation of long-wavelength hydrophobic carbon dots.

Specifically, some embodiments of the present invention provide a method for preparing carbon dots, which includes the following steps:

S1. Dissolving and mixing the carbon dot preparation raw materials in a solvent, and then removing the solvent capable of reacting with the dehydrating agent.

In some embodiments, the carbon dot preparation raw materials include but are not limited to carbon sources and nitrogen and sulfur co-doping agents. Further, the carbon source includes but not limited to at least one of citric acid, oxalic acid, sodium citrate, sodium oxalate, and glucose. Nitrogen, sulfur co-doping agents include but not limited to D,L-homocysteine, L-methionine, L-cysteine, L-cysteine hydrochloride, D-cysteine acid, glutathione, N-acetyl-L-cysteine, β-mercaptoethylamine and thioacetamide.

In some preferred embodiments, the nitrogen and sulfur co-doping agent includes at least one of L-cysteine, L-cysteine hydrochloride and N-acetyl-L-cysteine. In some preferred embodiments, the mass ratio of the carbon source to the nitrogen and sulfur co-doping agent is 1:0.5-10.

Alternatively, the carbon dot preparation raw materials include ethylenediamine, polyethyleneimine, phenol and the like.

In some embodiments, the solvent used to dissolve the raw materials for preparing carbon dots is water. Dissolving and mixing the raw materials for preparing carbon dots in the solvent and then removing the solvent includes: co-dissolving the raw materials for preparing carbon dots in water, and then dissolving the raw materials for preparing carbon dots in water. °C for 6-15 hours, preferably, the water is ultrapure water. That is, after the carbon dot preparation raw material is completely dissolved in water, wherein the carbon dot preparation raw material is preferably a powder, the water is evaporated by heating to obtain a solid homogeneous mixture without water or a slurry homogeneous mixture containing a small amount of water.

In some embodiments, the vessel for dissolving and removing the solvent is selected from any one of a polytetrafluoroethylene reaction liner, a beaker and a round bottom flask. Preferably, the container is a polytetrafluoroethylene reactive liner.

S2. Add a dehydrating agent to the homogeneous mixture of carbon dot preparation raw materials, and react at a temperature of 80-200°C.

In some embodiments, the reaction time is 10-360 min, preferably 20-200 min, more preferably 20-80 min. By controlling the above reaction time, the raw materials can be fully reacted to obtain carbon dots with better quality.

Further, according to the proportion and quality requirements of hydrophobic carbon dots, in some embodiments, the amount of dehydrating agent can be 0.1-1 g.

Further, in some embodiments, dehydrating agents include but are not limited to polyphosphoric acid, N,N'-dicyclohexylcarboimide (DCC), 1-(3-dimethylaminopropyl)-3-ethane Ethylcarbimide (EDC), 1-(3-dimethylaminopropyl)-3-ethylcarbimide hydrochloride (EDCI), N,N-dimethylformamide, 2,2 -Dichloro-5-(2-phenylethyl)-4-(trimethylsilyl)-3-furanone (DPTF), 1,3-dimethyl-2-imidazolinone (P-DMI), Bis(trichloromethyl)carbonate (BTC), thionyl chloride-dimethylformamide (SOCl ₂ -DMF), 2-chloro-1,3 dimethyl imidazolium chloride (DMC), pentachloro At least one of phosphorus chloride, phosphorus oxychloride and phosphorus pentoxide.

In some preferred embodiments, the dehydrating agent is N,N'-dicyclohexylcarbimide, 1-(3-dimethylaminopropyl)-3-ethylcarbimide or 1-(3 -Dimethylaminopropyl)-3-ethylcarbimide hydrochloride.

Specifically, the dehydrating agent is mostly solid, therefore, in order to enable the dehydrating agent to fully contact with the carbon dot preparation raw materials, therefore, in some embodiments, the dehydrating agent is added in the form of an organic solution, preferably for The organic solvent for dissolving the dehydrating agent is acetonitrile, but the amount of organic solvent used for dissolving the dehydrating agent is very small, only 100-1000uL, which will not substantially affect the reaction system. After the removal, the process of adding a dehydrating agent to carry out the reaction is not carried out in an organic solvent as a whole. In addition, when the dehydrating agent is a liquid dehydrating agent, there is no need to add an organic solvent to dissolve the dehydrating agent.

Further, in some embodiments, the reaction vessel used for preparing carbon dots is selected from any one of a hydrothermal reaction kettle, a beaker and a round bottom flask. In a preferred embodiment, the reaction vessel is a hydrothermal reaction kettle.

In some embodiments, the heating container used for heating and maintaining the reaction temperature is selected from any one of a water bath, an oil bath, and an electric constant temperature blast drying oven. In a preferred embodiment, the heating container is an electric heating constant temperature blast drying oven.

Further, since the carbon dots directly generated by the synthesis reaction are solids in a consolidated state in which water-soluble carbon dots and hydrophobic carbon dots are mixed, in some embodiments, the following optional steps may also be included:

S3. The carbon dot solid obtained by the reaction is dissolved with a solvent to obtain a carbon dot solution.

In some embodiments, since the carbon dot solid includes both water-soluble carbon dots and hydrophobic carbon dots, the carbon dot solid is dissolved in a water-soluble solvent and a hydrophobic solvent, respectively, to obtain a solution of water-soluble carbon dots and a solution of hydrophobic carbon dots , and then remove the solvent to obtain water-soluble carbon dots and hydrophobic carbon dots. That is, when the solvent is water, the carbon dots in the carbon dot solution are hydrophilic carbon dots, and the remaining solid is extracted by the corresponding solvent to obtain hydrophobic carbon dots; and the hydrophobic carbon dots that can dissolve hydrophobic carbon dots are used. When dissolved in a neutral solvent, the obtained carbon dot solution is the hydrophobic carbon dot solution, and the remaining solid is extracted with pure water to obtain water-soluble carbon dots. Therefore, the water-soluble carbon dots and hydrophobic carbon dots can be separated by solvent dissolution and extraction to obtain separate water-soluble carbon dots and hydrophobic carbon dots.

It should be noted that the method of removing the solvent from the carbon dot solution to obtain the carbon dots includes but not limited to rotary evaporation or freeze drying.

Specifically, in some embodiments, the water-soluble solvent is water, and the hydrophobic solvent is an organic solvent, and the organic solvent includes but is not limited to at least one of cyclohexane, carbon tetrachloride, chloroform, tetrahydrofuran, and methanol. Preferably, the hydrophobic solvent is chloroform.

It should be noted that when water is used to solvent carbon dots to prepare raw materials in the embodiment, the use of organic solvents is avoided in the entire synthesis process, which is environmentally friendly and green. In contrast, other existing synthetic methods use organic solutions and need to be heated, and the organic solutions are volatile when heated, and there are potential safety hazards. In the separation stage of the embodiment of the present invention, it is necessary to use an organic solvent to extract and dissolve, but without heating.

Some embodiments of the present invention also provide a carbon dot, which is prepared by the method for preparing carbon dots in any of the foregoing embodiments. In some preferred embodiments, the carbon dots are hydrophobic carbon dots isolated after the reaction. Further, the hydrophobic carbon dots may also be N, S co-doped hydrophobic carbon dots with a fluorescence emission wavelength of 450-540 nm.

Some embodiments of the present invention also provide the application of the above-mentioned carbon dots in the preparation of fluorescent materials.

Some embodiments of the present invention also provide the application of carbon dots in the preparation of solid-state lighting devices, displays or solid luminescent shaping materials, where the carbon dots are hydrophobic carbon dots separated after reaction.

Some embodiments of the present invention also provide a solid luminescent excipient material, the raw material components of which contain the above-mentioned hydrophobic carbon dots.

The characteristics and performance of the present invention will be described in further detail below in conjunction with the examples.

Example 1

(1) Place citric acid and L-cysteine hydrochloride in the polytetrafluoroethylene lining, add 2mL of ultrapure water in the lining to make it dissolve and mix evenly, the amount of citric acid is 0.4mmoL, the amount of substance of L-cysteine hydrochloride was 0.5mmoL. The lining is placed in an electrothermal constant temperature blast drying oven at 70°C for 12 hours.

(2) Add 0.3g of N,N'-dicyclohexylcarboimide (DCC) to the inner lining of step (1), put the inner lining into a hydrothermal reaction kettle and place it in an electric constant temperature blast drying oven React at 180° C. for 40 minutes to obtain a dark brown solid product (as shown in FIG. 1 ).

(3) The solid product is ultrasonically dissolved with chloroform to obtain a hydrophobic carbon dot solution, and then rotary evaporated to obtain a hydrophobic carbon dot solid. Use 10ml of pure water to ultrasonically extract the solid insoluble in chloroform multiple times to obtain the aqueous solution of hydrophilic carbon dots, and obtain the hydrophilic carbon dot solid by freeze-drying.

Example 2

(1) Put sodium citrate and D,L-homocysteine in a beaker, add 2mL of ultrapure water to the beaker to dissolve and mix evenly, the amount of sodium citrate is 0.6mmoL, D , The amount of L-homocysteine substance is 1mmoL. The beaker was placed in an electric thermostat blast drying oven at 70°C for 6h.

(2) Add 0.5g 1-(3-dimethylaminopropyl)-3-ethylcarboximide (EDC) to the beaker of step (1), continue to be placed in an electric heating constant temperature blast drying oven for 200 °C for 10 min to obtain a yellow solid (as shown in Figure 2). Use pure water to sonicate the yellow solid in multiple steps to obtain a blue luminescent hydrophilic carbon dot solution, and freeze-dry to obtain a hydrophilic carbon dot solid. Part of the product that cannot be dissolved in pure water is completely dissolved in methanol to obtain a hydrophobic carbon dot solution, and a hydrophobic carbon dot solid is obtained after rotary evaporation.

Example 3

(1) Oxalic acid and N-acetyl-L-cysteine are placed in a round-bottomed flask, and 2 mL of ultrapure water is added to the round-bottomed flask to dissolve and mix uniformly. The amount of oxalic acid is 1.2mmoL, The amount of N-acetyl-L-cysteine substance was 1 mmoL. The beaker was placed in an electric thermostat blast drying oven at 70°C for 10 h.

(2) Add 0.5g of 1,3-dimethyl-2-imidazolidinone to the round-bottomed flask in step (1), place it in a water bath at 100°C for 5 hours, and obtain a brownish-yellow solid (as shown in Figure 3 ). The solid is ultrasonically dissolved with chloroform several times to obtain a hydrophobic carbon dot solution, and methanol is added to the solution and centrifuged to obtain a hydrophobic carbon dot solid. Solids that cannot be dissolved in chloroform solution are dissolved in pure water to obtain a hydrophilic carbon dot aqueous solution. After adding isopropanol to the aqueous solution, centrifuge at 8000 rpm to obtain a hydrophilic carbon dot solid.

Example 4

(1) Citric acid and polyethylenimine are placed in a round-bottomed flask, and the mixed reagent of 2 mL of ultrapure water and ethanol is added to the round-bottomed flask to dissolve and mix the raw materials evenly. The amount of substance was 1.0 mmoL, the amount of substance of polyethyleneimine was 2.8 mmoL. The round-bottomed flask was placed in an electric thermostat blast drying oven at 70°C for 3 h.

(2) Add 0.2 g of bis(trichloromethyl)carbonate (BTC) to the round-bottomed flask in step (1), place the round-bottomed flask in a medium oil bath at 170°C for 2 hours to obtain a dark brown solid, Dissolve in chloroform to obtain a hydrophobic carbon dot solution, add acetonitrile and centrifuge to obtain a hydrophobic carbon dot solid. The carbon dots emit yellow light, the best emission wavelength is 543nm, and the quantum yield is 18%. The remaining insoluble solids were dissolved in pure aqueous solution to obtain an aqueous solution of blue luminescent hydrophilic carbon dots. After adding acetonitrile to the aqueous solution and centrifuging and drying, a hydrophilic carbon dot solid was obtained. The optimal emission wavelength was 431nm and the quantum yield was 22 %.

Comparative example 1

(1) Place citric acid and L-cysteine hydrochloride in the polytetrafluoroethylene lining, and fully stir and mix with a glass rod. The amount of citric acid is 0.4mmoL, and the amount of L-cysteine The amount of the salt of the substance was 0.5mmoL.

(2) Add 0.3g of N,N'-dicyclohexylcarboimide (DCC) to the inner lining of step (1), put the inner lining into a hydrothermal reaction kettle and place it in an electric constant temperature blast drying oven After reacting at 180°C for 40 minutes, a pale yellow solid product was obtained. The solid product was ultrasonically dissolved with chloroform to obtain a hydrophobic carbon dot solution, and then rotary evaporated to obtain a hydrophobic carbon dot solid. Dissolve the remaining insoluble solids with water to obtain a blue luminous water-soluble carbon dot solution, and freeze-dry to obtain a water-soluble carbon dot solid.

Comparative example 2

The only difference between this comparative example and Example 1 is that the reaction temperature of step (2) is 60 degrees, the reaction time is 30 minutes, and a light yellow solid product can be prepared, which can be ultrasonically soluble in water and turn blue Chromatic fluorescence, that is, only hydrophilic carbon dots can be prepared.

It should be noted that, in the above examples and comparative examples, when the dehydrating agent is solid, it should be dissolved in 200 uL of acetonitrile first, and then added into the reaction kettle.

Comparative example 3

The only difference between this comparative example and Example 1 is that in step (2), no dehydrating agent is added, and the reaction is carried out directly. The product is a brown-yellow solid, and the carbon dots are only blue-emitting hydrophilic carbon dots.

Test example 1

The hydrophobic carbon dot solution in Example 1 is irradiated under 365nm ultraviolet light, as shown in Figure 4, it emits yellow light, and obtains the fluorescence emission figure and UV-visible absorption spectrum figure of the hydrophobic carbon dot in Example 1 , as shown in Figure 5 and Figure 6, the results show that the hydrophobic carbon dots have an optimal emission wavelength of 540nm and a maximum absorption wavelength of 352nm, but there is a wide absorption between 400nm and 500nm, and the fluorescence quantum yield is 30%. Then by X-ray photoelectron spectroscopy (XPS), the hydrophobic carbon dot in embodiment 1 has been carried out elemental analysis, and the result is as shown in Figure 7, and the result shows that carbon dot contains four kinds of elements: C, N, O, S , belonging to N, S co-doped hydrophobic carbon dots. The hydrophilic carbon dot solution in Example 1 was irradiated under 365nm ultraviolet light, as shown in Figure 8, it emitted blue light. Its fluorescence spectrum and ultraviolet-visible absorption spectrum are shown in Figure 9 and Figure 10, the optimum emission wavelength is 450nm, the maximum absorption wavelength is 352nm, and the quantum yield is 34%.

The carbon dot of Comparative Example 1 is analyzed, as shown in Figure 11, its hydrophobic carbon dot is blue light, as can be seen from the fluorescence emission spectrum of the hydrophobic carbon dot of Comparative Example 1 shown in Figure 12, the maximum The emission wavelength is 440nm, and the quantum yield is 11%. As shown in Figure 13 and Figure 14, the photos and fluorescence emission spectra of the hydrophilic carbon dot solution of the water-soluble carbon dot solution of Comparative Example 1 under 365nm ultraviolet light irradiation can be seen , which emits blue light with a maximum emission wavelength of 448 nm and a quantum yield of 14%.

Through the comparison of Example 1 and Comparative Example 1, it can be seen that if the carbon source and N, S doping reagent are fully dissolved and mixed evenly without adding solvent in the first step, when the dehydrating agent is directly added for reaction, it is not conducive to N, S co-doping The synthesis of carbon dots (most of the dehydrating agent only reacts with one kind of raw material), the synthesis efficiency is low, the emission wavelength of the prepared hydrophobic carbon dots is obviously shortened, and the quantum yield is low.

Test example 2

The hydrophobic carbon dots obtained in Example 1 exhibit excellent fluorescence properties, and can be used in solid-state lighting and displays. As shown in Figure 15, the hydrophobic carbon dots are used as one of the light source components to construct a white light illumination LED lamp. Fig. 16 is a diagram of the electroluminescence spectrum of the manufactured white LED device. Consists of two emission bands: blue λem at 450nm, from the blue GaN-based chip, and a broad yellow emission at 575nm from hydrophobic carbon dots. The two emission bands mix to produce white light. The CIE of the prepared white LED is (0.2637, 0.2255), which falls within the range of the white light region. These results demonstrate the successful fabrication of white LEDs based on yellow-emitting hydrophobic carbon dots.

Test example 3

The application of the hydrophobic carbon dots in Example 1 in the production of solid luminescent shaping materials. Mix transparent epoxy resin A and epoxy resin B at a mass ratio of 3:1, add an appropriate amount of hydrophobic carbon dot solution, mix evenly again, pour it into a mold, and let it stand at room temperature for 24 hours to obtain the mixture shown in Figure 17 and The solid luminescent shaping material shown in FIG. 18 . The material is a hard solid material, and brown color can be observed under sunlight (as shown in FIG. 17 ). Under the irradiation of 365nm ultraviolet light, the solid emits yellow fluorescence (as shown in Figure 18).

Test example 4

The hydrophilic carbon dot solution in Example 2 was irradiated under 365nm ultraviolet light, as shown in FIG. 19 , it emitted blue light. The hydrophobic carbon dot solid in Example 2 was used to obtain a fluorescence emission spectrum, as shown in FIG. 20 , the fluorescence emission wavelength is 490 nm, and the fluorescence quantum yield is 19%. The hydrophobic carbon dot solution in Example 3 was irradiated with 365nm ultraviolet light, as shown in FIG. 21 , it emitted green light, the optimum emission wavelength was 530nm, and the quantum yield was 21%. The hydrophilic carbon dots obtained in Example 3 also emit blue light, the optimum emission wavelength is 426nm, and the quantum yield is 33%.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (18)

1. A preparation method of carbon dots, characterized in that it comprises: Add a dehydrating agent to the homogeneous mixture of carbon dot preparation raw materials, and react at a temperature of 100~200°C; Wherein, the carbon dot preparation raw material contains a hydrophilic group, and the homogeneous mixture is mainly obtained by the following preparation steps: co-dissolving the carbon dot preparation raw material in water, and then reacting at 60~80°C for 6~15h; The carbon dot preparation raw materials include carbon source and nitrogen, sulfur co-doping agent, the carbon source is at least one of citric acid, oxalic acid, sodium citrate sodium oxalate; the nitrogen, sulfur co-doping agent is D , in L-homocysteine, L-cysteine, L-cysteine hydrochloride, D-cysteine, glutathione, N-acetyl-L-cysteine At least one; the mass ratio of the carbon source to the nitrogen and sulfur co-doping agent is 1:0.5~10; The dehydrating agent is N, N'-dicyclohexyl carboximide, 1-(3-dimethylaminopropyl)-3-ethylcarboximide, 1-(3-dimethylaminopropyl base)-3-ethylcarbimide hydrochloride, 1,3-dimethyl-2-imidazolidinone, bis(trichloromethyl)carbonate; the amount of dehydrating agent 0.1-1 g. 2. preparation method according to claim 1, is characterized in that, the time for reacting is 10～360 min. 3. The preparation method according to claim 1, characterized in that, the dehydrating agent is added in the form of an organic solution. 4. The preparation method according to claim 3, characterized in that, the organic solvent used to dissolve the dehydrating agent is acetonitrile. 5. preparation method according to claim 1 is characterized in that, the reaction container that is used to prepare carbon dot is selected from any one in hydrothermal reaction still, beaker and round bottom flask. 6. preparation method according to claim 1 is characterized in that, is used for heating and keeps the heating container of reaction temperature to be selected from any one in water bath pan, oil bath pan and electric heating constant temperature blast drying oven. 7. preparation method according to claim 1 is characterized in that, described water is ultrapure water. 8. The preparation method according to claim 1, wherein the container for dissolving and removing the solvent is selected from any one of a polytetrafluoroethylene reaction liner, a beaker and a round bottom flask. 9. The preparation method according to any one of claims 1 to 6, wherein the preparation method further comprises dissolving the carbon dot solid obtained by the reaction with a solvent to obtain a carbon dot solution. 10. The preparation method according to claim 9, characterized in that, the preparation method further comprises removing the solvent from the carbon dot solution to obtain carbon dot powder. 11. preparation method according to claim 10 is characterized in that, dissolves described carbon dot solid with water-soluble solvent and hydrophobicity solvent respectively, to obtain the solution of water-soluble carbon dot and the solution of hydrophobic carbon dot, removes respectively again The solvent obtains water-soluble carbon dots and hydrophobic carbon dots. 12. preparation method according to claim 11, is characterized in that, described water-soluble solvent is pure water, buffer solution, and described hydrophobic solvent is organic solvent, and described organic solvent comprises cyclohexane, carbon tetrachloride , at least one of chloroform, tetrahydrofuran and methanol. 13. A carbon dot, characterized in that it is prepared by the preparation method according to any one of claims 1 to 12. 14. The carbon dot according to claim 13, characterized in that, the carbon dot is a hydrophobic carbon dot separated after reaction. 15. The carbon dot according to claim 14, wherein the hydrophobic carbon dots are N, S co-doped hydrophobic carbon dots with a fluorescence emission wavelength of 450-580 nm. 16. Use of the carbon dots according to any one of claims 13 to 15 in the preparation of fluorescent materials. 17. The application of the carbon dots according to claim 16 in the preparation of solid-state lighting devices, displays or solid luminescent excipient materials, wherein the carbon dots are hydrophobic carbon dots separated after reaction. 18. A solid luminescent shaping material, characterized in that its raw material components contain the hydrophobic carbon dots according to any one of claims 14-15.

Images